KR0168448B1 - Apparatus and method for reducing noise in high frequency band - Google Patents

Abstract

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Description

High Frequency Noise Reduction Device and Its Reduction Method

1 is a diagram showing a recording signal and a frequency spectrum of a current video disc record.

2A is a diagram for explaining the frequency distribution of recording signals of a current video disc record.

2B, 2C, and 2D are diagrams for explaining the frequency distribution of recording signals of high-definition video disc records.

3 is a diagram showing frequency characteristics of a reproduction signal of a conventional CAV disc.

4 is a block diagram showing the configuration of a conventional video disc playback system.

FIG. 5 is a diagram for explaining the double and triple waves generated during the reproduction of a conventional video disc record. FIG.

6A, 6B, 6C, and 6D show the frequency spectrum of the RF signal when no zone amplification correction is performed.

7A, 7B, 7C and 7D show the frequency spectrum of the RF signal when the zone amplification correction is performed.

8 is a block diagram showing an overall configuration of a regeneration circuit according to an embodiment of the present invention.

FIG. 9 shows the relationship between beam spots and bits in the embodiment of FIG. 8. FIG.

10A, 10B, 10C, 10D, and 10E show the frequency spectrum of the RF signal obtained in each part of the reproduction circuit of FIG. 8 when the rise of the high range is suppressed by the de-emphasis circuit. Figure shown.

11A, 11B, 11C, and 11D show the frequency spectrum of the RF signal obtained in each part of the reproduction circuit of FIG. 8 when the rise of the high frequency component cannot be suppressed by the de-emphasis circuit. .

12 is a detailed circuit diagram of a high pass correction filter.

13A and 13B are diagrams for explaining the operation of the high pass correction filter when a high frequency signal is applied.

14A and 14B are diagrams for explaining the operation of the high pass correction filter when a low frequency signal is applied.

FIG. 15A is a diagram showing frequency characteristics and group delay characteristics of a high pass correction filter. FIG.

15B is a diagram showing the amplitude characteristics of the high pass correction filter, and the vertical axis represents the decimal ratio.

16 is a detailed circuit diagram of the limiter and duty compensation circuit.

17 is a specific circuit diagram of the main de-emphasis circuit.

* Explanation of symbols for main parts of the drawings

3: 4-split sensor 4, 5, 7: adder

6: fixed delay circuit 8: variable delay circuit

9: 90 ° ideal phase 10: phase detector

11, 32: preamp 12: high pass correction filter

15 narrowband pass filter 16 wideband pass filter

18, 34: limiter 19: duty correction circuit

20: FM detection circuit 21: low pass filter

22: de-emphasis circuit 23: level shift

31: pickup 33: high-pass amplification correction circuit

35: FM demodulation circuit

This application is related to pending application number 321,821, filed on March 10, 1989 and owned by the assignee of the present invention.

The present invention relates to a high frequency noise reduction device and a high frequency noise reduction method, and more particularly, to an apparatus and method for correcting a frequency distribution caused by pickup and transmission distortion, used in an optical video disc player.

A current optical video disc player for optically reproducing a video disc recorder in which NTSC color video signals are optically recorded is disclosed in detail in, for example, a laser disc technical book published by Asuki Corporation on November 1, 1986.

EMBODIMENT OF THE INVENTION Hereafter, embodiment of this invention is described in detail with reference to an accompanying drawing.

As shown in the frequency spectrum diagrams of FIGS. 1 and 2A, the optical video disc record has FM shifted by FM modulating the NTSC color video signal such that the sync chip is 7.6 MHz, the pedestal level is 8.3 MHz, and the white peak is 9.3 MHz. The inverse, upper and lower bands are recorded as modulated video signals in the range of 4 MHz-13.5 MHz. In this video disc record, a carrier of 2.3 MHz and a carrier of 2.8 MHz are FM-modulated by two audio signals. On the low side of the FM audio signal, a digital audio signal having the same form as that of a compact disc record is recorded by frequency multiplexing.

By the way, in recent years, the image | video high resolution is required | required further, In order to cope with high-definition while maintaining the rotational speed of a disk as it is, ie, the center frequency, it is necessary to enlarge the frequency band of a video signal. As a method for expanding the band of the video signal, three methods shown in FIGS. 2B to 2D may be considered.

FIG. 2B shows a method (first method) of expanding the low and high frequencies together by deleting the FM voice signal. FIG. 2C shows a method of expanding only the high range while maintaining the FM audio signal as it is, and doubling the energy of the high range (second method). FIG. 2D shows a method of deleting only the FM voice signal to enlarge only the low range and to double the low range energy (third system). In the second and third systems, it is necessary to double the energy of the high or low band only, so that the processing of the video signal in the RF stage at the time of recording on the disc becomes more complicated than the processing by the first method. Therefore, it is technically impossible to realize a filter that satisfies the frequency characteristics shown in FIGS. 2C and 2D. As a result, by adopting the first method, it is most consistent to realize high deterioration.

By the way, when the optical signal is reproduced using a normal pickup, since the spot of the laser light is larger than the pit width of the disc, the resolution for detecting the signal is lowered, thereby reproducing as shown in FIG. The high frequency component of the RF signal is degraded. This tendency is more pronounced in constant angular velocities (CAV) discs where the angular velocity is closer to the inner circumference of the disc and the higher the frequency. In CAV discs, the linear velocity varies from 10.75 m / s to 32 m / s from inner to outer. For this reason, the length of the signal detected in unit time at the outer periphery is also longer than the length at the inner periphery even for signals with the same length pits. The length of the signal detected in unit time at the outermost circumference is three times the length at the innermost circumference. Therefore, the deterioration of the high frequency component of a reproduction RF signal is more prominent in the inner peripheral side of a CAV disc.

In a CLV (Constant Linear Velocity) disk having a constant linear velocity, a high-frequency deterioration in which the high-band deterioration in the inner circumference of the CAV disk occurs over the entire circumference.

As described above, since the deterioration of the frequency characteristic in the high range is remarkable in the RF signal obtained by the pickup, the method disclosed in pages 77 to 79 of the above laser disk technical book has been conventionally used. This method is shown in FIG. Referring to FIG. 4, the RF signal detected by the pickup 31 is amplified by the preamplifier 32. A high frequency amplification correction circuit 33 is inserted between the preamplifier 32 and the limiter 34 to correct the deterioration of the frequency characteristic at the high frequency. The high frequency amplification correction circuit 33 performs high frequency amplification correction for raising the high frequency component of the RF signal. The output signal of the limiter 34 is demodulated to a color image signal in the FM demodulation circuit 35.

However, the above-described high frequency amplification correction has a problem. As described above, the frequency distribution of the recording signal of the conventional optical video disc is shown in FIG. 2A. Since the FM modulated signal passes through the limiter at the time of recording, the reproduced RF signal includes the double and triple waves shown in FIG. In addition, a double wave also occurs due to distortion of the transmission system and the circuit system from the pickup. Such a double wave is likely to overlap the high frequency portion in the band of the fundamental wave as shown in FIG. In particular, with respect to the high-definition video disc record in which the band of the video signal is expanded to the low side and the high side in the frequency distribution of the recording signal shown in FIG. 2B, the enlargement of the signal wave is limited to the expansion of the conventional signal wave. It becomes the enlarged state which added the oblique part of 5 degree | times. As a result, the superposition of the fundamental wave and the double wave becomes remarkable. If such a signal is detected as it is during playback, i.e., FM demodulated, this overlap appears on the screen as bits or noise.

In addition, since the resolution of signal detection is low in the inner circumference of the CAV disc or the circumference of the CLV disc, the high frequency component is unlikely to appear at the time of reproduction. If correction is made so that the high frequency component rises, the S / N deteriorates and the image quality deteriorates.

Next, a signal in which the high frequency component deteriorates in the inner circumference of the CAV disk or the circumference of the CLV disk will be described in detail with reference to FIGS. 6A to 6D and 7A to 7D.

6A to 6D show the frequency spectrum of the RF signal when high pass amplification is not corrected. The RF signal as shown in FIG. 6A includes the carrier C and the high range is degraded. When such an RF signal passes through the limiter, the upper band component H and the lower band component L shown in FIG. 6C are averaged and outputted. The ratio of carriers to the sidebands is almost unchanged, but the doubled wave (W) that existed only in the high range and the bit (Y) due to the overlap of the double wave and the fundamental wave are also averaged. For this reason, when the output signal of the limiter is FM demodulated, bits and noise are generated in the high range as shown in FIG. 6D.

7A to 7D show the frequency spectrum of the RF signal when the high pass amplification is corrected. Similarly to Fig. 6A, the RF signal shown in Fig. 7A is corrected by the high pass amplification correction circuit 33 so that the high pass component is raised. As a result, the bit Y existing only in the high range is also amplified. The RF signal then passes through the limiter 34, so that the noise and bits shown in FIG. 7C are also amplified. FM demodulation results in degradation of S / N and amplification of bits in the high range as shown in FIG. 7d.

And, in FIGS. 6A to 6D and 7A to 7D, 0 represents a voice bit. Also, FIG. 6B is exactly the same as FIG. 6A.

As described above, if the high frequency component of the reproduced RF signal is simply raised, deterioration of the high frequency component can be prevented. On the contrary, deterioration of S / N and augmentation of bits occur in the high frequency, resulting in an unsightly screen.

It is an object of the present invention to provide a high frequency noise reduction device capable of reducing high frequency noise of a reproduced FM signal.

Another object of the present invention is to provide a method capable of reducing high frequency noise of a reproduced FM signal.

It is yet another object of the present invention to provide an apparatus and method which can prevent degradation of high frequency components of reproduction RF signals from an optical video disc player and at the same time prevent degradation of S / N and enhancement of bits at high frequencies. It is for.

The high pass noise reduction prevention according to the present invention is provided with a high pass correction device for lowering the high frequency components of the reproduced FM signal, and a limiter for limiting the amplitude of the output signal of the high pass correction device.

According to the high frequency noise reducing device, before the RF signal is input to the limiter, the high frequency component of the RF signal is lowered, and the noise and bit components are lowered. This makes it possible to obtain a good signal of S / N with less influence of noise and bits.

According to another aspect of the present invention, the high pass noise reduction device is also equipped with a duty correction device. The duty cycle correction device corrects the duty of the output signal of the limiter so that the direct current component is not included in the output signal of the limiter. This prevents the generation of double waves in the output signal of the limiter.

According to another aspect of the present invention, the high pass noise reducing device includes an FM detector for FM detection of the output signal of the limiter, a low pass filter for passing a predetermined low pass component among the output signals of the FM detector, and a high pass of the output signal of the low pass filter. It also has a de-emphasis device that attenuates the components.

This makes it possible to suppress an increase in the high frequency component due to an abnormality in the carrier ratio with respect to the sideband.

According to another aspect of the present invention, the high pass noise reduction device is also provided with first and second band pass filters and switches connected in parallel between the high pass correction device and the limiter. The first band pass filter has a first pass band, and the second band pass filter has a second pass band wider than the first pass band. The switch selects one of the first and second band pass filters, applies the output signal of the high pass correction device to the selected band pass filter, and gives the output signal of the selected band pass filter to the limiter.

This makes it possible to reproduce both the RF signal from the current optical video disc record and the RF signal from the high definition video disc record.

8 is a block diagram showing the overall configuration of a regeneration circuit according to an embodiment of the present invention. In FIG. 8, the four-segment sensor 3 constituting the pick-up is provided with the photodiodes B1 and B2 on the leading side and the trailing side with respect to the tangential direction of the track on the disc, that is, the traveling direction (arrow mark Q) of the pit. It consists of diodes B3 and B4.

The output signals photoelectrically converted into the preceding photodiodes B1 and B2 are input to the adder 4 and added to each other. The output signals photoelectrically converted by the trailing side photodiodes B3 and B4 are input to the adder 5 and added to each other.

The output signal of the adder 5 is delayed by the fixed delay time t1 selected by the fixed delay circuit 6 and then input to the adder 7. The output signal of the adder 4 is input to the adder 7 after being delayed by the delay time T by the variable delay circuit 8. These output signals are added to each other by the adder 7 and output as reproduction RF signals.

In addition, the output signal delayed by the variable delay circuit 8 is abnormally set to 90 degrees by a 90 degrees phase shifter 9 (pbase shifter). The 90 ° phase shifter 9 is commonly used to compare two signal phases at the same frequency. The phase of the output signal of the 90 ° phase shifter 9 is compared with the phase of the output signal of the fixed delay circuit 6 by the phase detector 10. The output signal of the phase detector 10 is fed back to the variable delay circuit 8 as a control signal SC corresponding to the phase difference of those output signals.

The delay time T of the variable delay circuit 8 changes in response to the control signal SC, and the delay time (so that the phase difference is zero, that is, the output signals of both delay circuits 6 and 8 always have exactly the same phase) T) is controlled.

Thus, in terms of electrical signal processing, the positional relationship between the beam spot and the bit becomes as shown in FIG. In FIG. 9, P represents pit. The beam spot portion electrically detected by the preceding side photodiodes B1 and B2 overlaps with the beam spot portion electrically detected by the trailing side photodiodes B3 and B4, and equivalently the beam spot diameter is 1 / It becomes two. As a result, the resolution capability of signal detection is improved, and the frequency characteristic of the detected RF signal is improved.

The fixed delay circuit 6 is added to correct the deviation of the control range according to the minimum delay amount of the variable delay circuit 8. However, the fixed delay circuit 6 is omitted, and the delay time T of the variable delay circuit 8 is controlled so that the output signal of the variable delay circuit 8 and the output signal of the adder 5 have exactly the same phase. You may.

The reproduction RF signal output from the adder 7 is supplied to the high pass correction filter 12 through the preamplifier 11. The reproduction RF signal having the frequency distribution shown in FIG. 10A is corrected so that its high frequency component is attenuated by passing through the high pass correction filter 12 as in FIG. 10B.

6A and 7A, the high frequency component of the reproduced RF signal deteriorates, and the upper band component H shows a frequency distribution smaller than the lower band component L.

The regenerative RF signal, in which the high pass component is attenuated by the high pass correction filter 12, passes through a narrow band pass filter (BPF) 15 or a wide band pass filter (BPF) 16 through the switch 14, and again the switch ( It is input to the rear limiter 18 via 17).

Narrowband BPF 15 is used to extract RF signals from current optical video disc records (hereinafter referred to as LDs) having the frequency spectrum of FIG. 2A. On the other hand, the wideband BPF 16 is used to extract a reproduction RF signal from a high-definition video disc record (hereinafter referred to as EDLD) having a frequency spectrum of FIG. 2b. The switches 14 and 17 are converted in synchronization with the EDLD and LD change signals SL supplied from the system control circuit 24. If the disc record to be reproduced is an LD, a reproduction RF signal is input to the narrowband BPF 15 and the switches 14 and 17 are converted so that the output signal of the narrowband BPF 15 is supplied to the limiter 18. . On the other hand, if the disc record to be reproduced is an EDLD, the reproduction RF signal is input to the wideband BPF 16, and the switches 14 and 17 are converted so that the output signal of the wideband BPF 16 is supplied to the limiter 18.

The reproduction RF signal imparted at the switch 17 is corrected so that the high range is attenuated, as shown in FIG. 10B. When the regenerative RF signal of FIG. 10B passes through the limiter 18, as shown in FIG. 10C, the double wave W and the bit Y, which existed only in the high range, are vertically symmetric about the carrier C. Averaged and reduced. At the same time, the required upper band component (H) and the lower band component (L) are averaged together and those components are output.

The output signal of the limiter 18 is input to the duty cycle correction circuit 19 and the FM detection circuit 20. The limiter 18 outputs signals of opposite polarities. When the duty of the limiter 18 itself is shifted, a double wave is generated in the output signal of the limiter 18, thereby reducing the effect of reducing the high frequency noise of the reproduced RF signal. When the duty of the limiter 18 is shifted, the direct current component is superimposed on the output signal of the limiter 18. Thus, the duty cycle correction circuit 19 compares the magnitudes of the DC components included in the bipolar signals output from the limiter 18 with each other, and controls the DC potentials input to the limiter 18 so that the potential difference between those DC components disappears. do. As a result, the duty of the output signal of the limiter 18 does not shift, and generation | occurrence | production of a double wave is suppressed.

The output signal of the limiter 18 is FM detected by the FM detection circuit 20, and is then FM demodulated and outputted as a base band video signal by passing through the low pass filter (LPF) 21 again. The cutoff frequency of the LPF 21 is set to allow only video signals of the base band. Therefore, the output signal of the limiter 18 having the frequency distribution shown in FIG. 10C becomes an image signal of the base band of FIG. 10D.

However, the carrier component is also slightly deteriorated by the high frequency degradation in the reproduction RF signal shown in FIG. 10A. On the other hand, since the lower band component L hardly deteriorates, as shown in FIG. 10C, the level of the carrier C of the output signal of the limiter 18 and the upper and lower band components H and L, respectively, are shown. The ratio of to is different from the normal ratio. As a result, as shown in FIG. 10D, the high frequency component of the FM detected output signal is raised. That is, in FIG. 10C, the carrier component is slightly reduced under the influence of the high-pass deterioration as described above, and the level of the sideband with respect to the level of the carrier becomes too large.

Therefore, it is necessary to suppress the rise of the high range due to such an abnormality of the carrier / side wave by the de-emphasis circuit 22 of the next stage.

The level shift circuit 23 generates an output signal having a voltage value suitable for the control of the de-emphasis circuit 22 in response to the control signal SC output from the phase detection circuit 10. The voltage value of this output signal increases as the voltage value of the control signal SC is lower. That is, the voltage value of the output signal becomes higher as the delay time T of the variable delay circuit 8 becomes smaller, and conversely becomes lower as the delay time T becomes larger. For example, in a CAV disc, since the linear velocity changes according to the radial position of the disc, the output signals of the following photodiodes B3 and B4 based on the output signals of the preceding photodiodes B1 and B2 are referenced. The amount of delay, i.e., the phase difference of their output signals, changes with the radial position of the disk. As a result, the phase difference of the signal output from the delay circuits 6 and 8 becomes larger on the inner circumferential side of the CAV disc than the outer circumferential side, and the voltage value of the control signal SC becomes larger accordingly.

As a result, in the inner circumference where the deterioration of the high band is significant in the RF stage, the attenuation of the high band by the de-emphasis circuit 22 becomes larger than that of the outer circumference. Thus, as shown in FIG. 10D, the FM demodulated output signal whose high pass component is raised by the high pass correction filter 12 passes through the de-emphasis circuit 22, thereby as shown in FIG. 10E. The high range of the output signal is attenuated by the amount raised by the correction. In connection with this, the double wave W and the bit Y are further separated so that the influence of noise and the bit is further suppressed.

On the other hand, as in the outer circumferential side of the CAV disc, the case where the high frequency degradation of the reproduction RF signal is small is considered. For example, considering the case where there is no high frequency degradation of the regenerative RF signal of FIG. 11A, the output signals of the high pass correction filter 12 and the limiter 18 are as shown in FIGS. 11B and 11C. In FIG. 11C, the components of the double wave W existing only in the high range are averaged and output so as to be vertically symmetric about the carrier C. In FIG.

When the output signal of the limiter 18 is FM detected, as shown in FIG. 11D, the bits existing only in the high range are reduced. In addition, the levels of the upper and lower band components L and H of the output signal of the limiter 18 are average levels of the upper and lower band components of the regenerated RF signal after the high pass correction, and thus the upper and lower band components of the output signal of the limiter 18 The level of the lower band components L and H is lowered by the amount of high frequency attenuation compared to the levels of the upper and lower band components L and H of the reproduction RF signal of FIG. 11A. However, the level of the carrier C also decreases under the influence of the high pass correction. Therefore, the ratio between the level of the carrier C in the output signal of the limiter 18 and the respective levels of the upper and lower bands is not changed compared with those of the level ratio in the reproduction RF signal before the high pass correction. As a result, the level ratio maintains a normal value, and correction in the de-emphasis circuit 22 is unnecessary.

Therefore, the control signal SC voltage value is lowered when the high frequency degradation is unlikely to occur in the reproduction RF signal, that is, when the CAV disc is reproduced on the outer circumferential side, so that the voltage value of the output signal of the level shift circuit 23 becomes high. As a result, the correction by the de-emphasis circuit 22 is slightly suppressed, and the output signal of the de-emphasis circuit 22 becomes almost the same as the FM detected output signal of FIG. 10d.

The configuration of the high pass correction filter 12 will now be described with reference to FIG.

The high pass correction filter 12 includes a delay path composed of transistors Tr ₁ and Tr ₂ and a delay line 13, and through paths composed of transistors Tr ₂ and Tr ₃ . The regenerated RF signal is applied to the delay line 13 through the transistor Tr ₁ , is delayed by the delay line 13, and then output to the emitter of the transistor Tr ₄ . The regenerated RF signal is simultaneously output as it is through the transistors Tr ₂ and Tr ₃ and added to the signal output to the emitter of the transistor Tr ₄ . That is, the reproduction RF signal delayed by the predetermined delay time t2 in the delay path is added to the reproduction RF signal obtained as is by the through path. The capacitor C7 is inserted to remove the direct current component.

As shown in FIG. 13A, when the reproduction RF signal has a high frequency, the non-delayed reproduction RF signal (shown in dashed lines) and the reproduction RF signal delayed by a predetermined delay time t2 (shown in solid lines) Are added to each other, the frequency component disappears as shown in FIG. 13B.

On the other hand, as shown in FIG. 14A, when the reproduction RF signal has a low frequency, the output signal obtained by the addition of the non-delayed reproduction RF signal and the delayed reproduction RF signal is as shown in FIG. 14B. Thus, the high pass correction filter 12 has a function of attenuating only the high pass component of the reproduced RF signal in accordance with the delay time t2 of the set delay line 13.

For example, when t2 = 32-35 nsec, the amplitude characteristics of Figs. 15a and 15b are obtained. In this way, the high pass correction filter 12 is used as a filter which is attenuated as the amplitude of the reproduction RF signal becomes high in the vicinity of the frequency of about 16 MHz.

In FIG. 15A, L1 represents an amplitude characteristic when the vertical axis is expressed in decibels (dB), and L2 represents a group delay characteristic depending on frequency. FIG. 15B also shows the amplitude characteristics of the reproduced RF signal when the vertical axis represents the true ratio of the reproduced RF signal.

As a means of attenuating only the high pass component of the reproduced RF signal, it is also possible to simply use LPF as a high pass correction filter, replacing the complicated configuration as shown in FIG.

Now, with reference to FIG. 16, the specific structure of the limiter 18 and the duty cycle correction circuit 19 is demonstrated.

The limiter 18 includes transistors Tr ₅ and Tr ₆ constituting the differential amplifier. If the base potentials of the transistors Tr ₅ and Rr ₆ are different from each other, the duty of the output signals 01 and 02 of the limiter 18 is shifted. Thus, these output signals 01 and 02 pass through the low pass filter made of the resistor R1 and the capacitor C1 and the low pass filter made of the resistor R2 and the capacitor C2 to extract only the direct current portion. These direct currents are compared by transistors Tr ₇ and Tr ₈ . As a result, control is performed by returning the current IC to the input unit such that the potentials of the direct currents are equal to each other, that is, the duty of the output signals 01 and 02 is 50%.

For example, when the base potential of the transistor Tr ₅ is greater than the base potential of the transistor Tr ₆ , the base potential of the transistor Tr ₈ becomes larger than the base potential of the transistor Tr ₇ .

As a result, the collector current of the transistor Tr ₈ becomes larger than the collector current of the transistor Tr ₇ . As a result, the control current I _C flows in the direction of the arrow L so that the current IC lowers the base potential of the transistor Tr ₅ via the current mirror circuit composed of the transistors Tr ₉ -Tr ₁₂ .

In this way, the duty of the output signal of the limiter 18 is corrected.

The specific configuration of the de-emphasis circuit 22 will now be described with reference to FIG.

The de-emphasis circuit 22 is a kind of LPF composed of the variable capacitor diode D1, the resistors R11 and R12 and the capacitor C11 as shown in FIG. The de-emphasis circuit 22 has a characteristic as LPF and attenuation characteristic of a high frequency component in accordance with the sum of the capacitance value of the capacitor C11, the capacitance value of the variable capacitor diode D1, and the resistance values of the resistors R11 and R12. Changes finely

The output voltage from the level shift circuit 23 is applied to the cathode side of the variable capacitor diode D1. The capacitance of the variable capacitance diode D1 changes according to the reverse voltage applied in this way. As a result, the high pass correction amount by the de-emphasis circuit 22 is controlled.

When the inner periphery of the CAV disc or the periphery of the CLV disc is reproduced, when the phase difference of the signal output from the delay circuits 6 and 8 (see Fig. 8) becomes large, the voltage value of the control signal SC becomes large. As a result, the voltage value of the output signal of the level shift circuit 23 is lowered. As a result, the voltage in the reverse direction of the variable capacitor diode D1 decreases, and the capacitance of the variable capacitor diode D1 increases inversely. As a result, the attenuation amount of the high range by the de-emphasis circuit 22 acting as the LPF is increased by an increase in the capacitance of the variable capacitance diode D1. As a result, the high-frequency attenuation by the de-emphasis circuit 22 increases during reproduction of the inner circumferential side of the CAV disc and reproduction of the entire circumference of the CLV disc.

On the other hand, at the time of reproduction on the outer circumferential side of the CAV disc, the phase difference of the signal output from the delay circuits 6 and 8 (see FIG. 8) becomes small, and the voltage value of the control signal SC becomes low. Thereby, the voltage value of the output signal of the level shift circuit 23 becomes high. As a result, the reverse voltage of the variable capacitor diode D1 increases, and the capacitance of the variable capacitor diode D1 decreases inversely. As a result, the high-frequency attenuation amount in the de-emphasis circuit 22 serving as the LPF becomes small by the decrease in the capacitance of the variable capacitance diode D1. As a result, high frequency attenuation by the de-emphasis circuit 22 is suppressed at the time of reproduction on the outer circumferential side of the CAV disc.

In the above embodiment, if the characteristics of the high pass correction filter 12 are inclined linearly (integral ratio) in the band, deterioration of DG (differential gain) and DP (differential phase) does not occur. Do not.

According to the present invention described above, it is possible to suppress degradation of S / N and enhancement of bits in the high range while preventing degradation of the high range of the reproduced RF signal. Therefore, the high-definition disc on which the frequency band of the video signal is expanded and recorded is sufficiently possible.

Claims (8)

A high frequency noise reduction device for reducing high frequency noise of a reproduced FM signal, comprising: high frequency correction means (12) for lowering a high frequency component of the reproduced FM signal, and amplitude of an output signal of the high frequency correction means (12) On the basis of the result of comparing the magnitude of the DC component included in the bipolar signal output from the limiter means such that the limiter means 18 for limiting the value and the output signal of the limiter means 18 are not included in the output signal. And duty correction means (19) for controlling the DC potential input to said limiter means (18) to correct the output signal and duty of said limiter means (18). A high frequency noise reduction device for reducing high frequency noise of a reproduced FM signal, comprising: high frequency correction means (12) for lowering a high frequency component of the reproduced FM signal, and amplitude of an output signal of the high frequency correction means (12) The limiter means 18, the high-pass correction means 12 and the limiter means 18 are provided in parallel, and the first band pass means 15 has a first pass band. First and second band pass means (15 and 16) and the first and second band pass means (15 and 16), wherein the two pass pass means (16) have a second pass band wider than the first pass band. Switch means 14 and 17 for selecting one of them, giving the output signal of the high pass correction means 12 to the selected band pass means, and giving the output signal of the selected band pass means to the limiter means 18; High frequency, characterized in that it includes) Noise reduction device. A high frequency noise reduction device for reducing high frequency noise of a reproduced FM signal, comprising: high frequency correction means (12) for lowering a high frequency component of the reproduced FM signal, and amplitude of an output signal of the high frequency correction means (12) Limiter means (18) for limiting the number of light sources, and converts light from the optical recording medium in which the signal is recorded in the form of the pit (P) constituting the track into an electrical signal, Conversion means ( ₃ ) comprising first photoelectric conversion means (B ₁ and B ₂ ) and second photoelectric conversion means (B ₃ and B ₄ ) provided on a trailing side, said first photoelectric conversion means (B ₁ and The output signal of the delay means 8 and the second photoelectric conversion means B ₃ and B ₄ and the output of the delay means 8 that can delay the output signal of B ₂ ) and change its delay time. Detects a time difference of a signal and corresponds to the detected time difference A high frequency noise reduction device characterized in that it outputs a signal and said delay means (8) comprises time difference detecting means (10) for changing said delay time in response to said signal output from said time difference detecting means (10). . 4. The output device of the delay means (8) and the second photoelectric conversion means (B ₃ and B ₄ ) according to claim 3, wherein the delay means (8) responds to the signal output from the time difference detecting means (10). A high-frequency noise device, characterized in that to control the time difference of the output signal of the zero). 4. The FM detector (20) according to claim 3, wherein the FM detector (20) for detecting the output signal of the limiter means (18), the low pass means (21) for passing the low pass component of the output signal of the FM detector (20), Attenuation amount of the high frequency component by the de-emphasis means 22 in response to the de-emphasis means 22 for attenuating the high frequency component of the output signal of the low pass means 21 and the time difference detecting means 10. High frequency noise reduction device comprising a control means for controlling the (23). A reproducing apparatus for reproducing an optical recording medium in which a signal is recorded in the form of a pit (P) constituting a track, wherein the light from the optical recording medium is converted into an electrical signal, and the conversion means (3) converting means including a first photoelectric conversion means (B ₁ and B ₂₎ and second photoelectric conversion means (B ₃ and B ₄₎ is provided on the side of the trailing, which is installed on the side of the preceding with respect to the reproduction direction (3) Delay means 8 for delaying the output signals of the first photoelectric conversion means B ₁ and B ₂ , the delay time of the delay means 8, and the second photoelectric conversion means B _3. And detecting the time difference between the output signal of B ₄ ) and the output signal of the delay means 8 and outputting a signal corresponding to the detected time difference, wherein the delay time of the delay means 8 is the time difference detection means. When changed in response to the output signal of (10) A difference detecting means 10, adding means (7), the adding means (7) to each other adds the output signal and the output signal of the second photoelectric conversion means (B ₃ and B ₄₎ of said delay means (8) FM detection of the output signal of the high frequency correction means 12 which reduces the high frequency component of an output signal, the limiter means 18 which limits the amplitude of the output signal of the said high frequency correction means 12, and the limiter means 18; FM detection means 20, low pass means 21 for passing the low pass component of the output signal of the FM detection means 20, and de-emphasis means for attenuating the high pass component of the output signal of the low pass means 21. (22) and control means (23) for controlling the amount of attenuation of the high frequency component by said de-emphasis means (22) in response to said output signal of said time difference detecting means (10). 7. The high-pass correction means (12) and the limiter means (18) are installed in parallel, wherein the first band pass means (15) has a first pass band and the second band pass. The means 16 selects one of the first and second band pass means 16 and the first and second band pass means 15 and 16 having a second pass band wider than the first pass band. And switch means 14 and 17 for giving the output signal of the high pass correction means 12 to the selected band pass means and giving the output signal of the selected band pass means to the limiter means 18. A playback apparatus, characterized in that. 8. The limiter according to claim 7, wherein the limiter is based on a result of comparing the magnitudes of the integrals included in the bipolar signal output from the limiter means so that the DC signal is not included in the output signal of the limiter means. And duty correction means (19) for controlling the direct current potential input to the means (18) to correct the output signal and duty of the limiter means (18).

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